The present invention is directed to flexural pivots and has particular, although not exclusive, application to pivots used in scanners.
In some laser printers, a modulated laser beam is deflected by an oscillating mirror so that deflected beam scans back and forth across a charge-bearing surface that is subsequently used to impart an image to paper or some other medium. The mirror is mounted on an armature secured to a flexural pivot, a device that includes flexure members that deflect when the armature pivots. The armature-flexure system constitutes a high-Q resonant system into which energy is imparted by a magentic driver. This apparatus is referred to as an optical scanner.
One type of flexural pivot employed in scanners is llustrated in FIGS. 1A and 1B. Two flexure members 12 and 14 are secured at their lower ends by bolts 16 and 18 to a stationary base 20. Similar bolts 22 and 24 secure their upper ends to an armature 26, on which is mounted a mirror (not shown). FIG. 1A depicts the undeflected state of the flexural pivot, while FIG. 1B depicts a deflected state. The length of the flexure members 12 and 14 are chosen to achieve the desired deflection within the elastic limits of the material from which the flexure member is made. By orienting the two flexure members 12 and 14 at angles to each other, a cross-axis stiffness is achieved that is greater than that which would result if the planes of the flexure members 12 and 14 coincided.
In order to give the scanner system a high resonant frequency, the ratio of torsional stiffness to inertia must be high. In this regard, the bolts 22 and 24 detract significantly from the resonant frequency, since the inertia that they add is significant. FIG. 2 depicts a design that eliminates these bolts. In this design, the flexure members 28 and 30 are embedded in slots in an arcuate base 32 and soldered into place. The armature 34 is cylindrical, and the other ends of the flexure members 28 and 30 are similarly embedded and soldered into slots in the armature. This design eliminates the inertia penalty of the nuts, but the cylindrical armature 34 contributes its own inertia penalty.
It is an object of the present invention to increase the resonant frequency that can be achieved through the use of a flexural pivot.